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51.
L. Robin M. Cocks Leonid E. Popov 《Proceedings of the Geologists' Association. Geologists' Association》2019,130(6):677-690
The Early Ordovician brachiopods of south-west Wales (Pembrokeshire and Carmarthenshire) are identified, in most cases for the first time. That period is termed the local Arenig Stage in Britain, but it is now correlated with the Floian, Dapingian, and earlier half of the Darriwilian, which are more recently established international stages in the system of stratigraphical nomenclature. The rocks in south-west Wales were laid down as turbidites in a backarc basin which formed part of the margin of the relatively small independent microcontinent of Avalonia at that time. However, since the Rheic Ocean between Avalonia and the immense Gondwana continent was relatively narrow in the Arenig, the brachiopods reviewed here can be established to be part of the Mediterranean Province, which was also extensive in the higher-latitude sectors in and around Gondwana in the Early Ordovician. The 17 brachiopod species identified within the Arenig brachiopod faunas of south-west Wales are described, including the new species Aporthophyla prisca, Tritoechia bolohaulensis, Skenidoides pontyfennensis and Paurorthis? llangynogensis. 相似文献
52.
岩浆镍-铜-铂族元素(PGE)硫化物矿床是峨眉火成岩省地幔柱活动形成的两个重要的成矿系列之一[1~3].目前已发现的与峨眉火成岩省相关的40余个镍-铜-铂族元素硫化物矿床(或矿点)中,多数分布在内带[3,4].它们可分为:1)富Ni、Cu而贫PGE的Ni-Cu型(如力马河和清水河);2)富Ni,Cu且PGE中等的Ni-Cu-PGE型(如清矿山和黄草坪);3)贫Ni、Cu富PGE的PGE型(如金宝山和杨合武). 相似文献
53.
Xie-Yan?SongEmail author Leonid?V.?Danyushevsky Reid?R.?Keays Lie-Meng?Chen Yu-Shan?Wang Yu-Long?Tian Jia-Fei?Xiao 《Mineralium Deposita》2012,47(3):277-297
Eastern and western portions of the Jinchuan ultramafic intrusion have previously been interpreted as dismembered segments
of a single elongate intrusion by late faults. However, the different stratigraphic sequences of the two portions indicate
that they are originally two separate intrusions, referred to as Eastern and Western intrusions in this study. The Eastern
intrusion is characterized by a concentric distribution of rock types with a core of sulfide dunite enveloped by lherzolite,
whereas the Western intrusion is composed of the Upper and Lower units, interpreted as magmatic mega cycles with regular variations
in lithology and chemistry. In the Western intrusion, the Upper unit consists of fine-grained dunite, lherzolite, and pyroxenite
from its base to its top. The MgO contents decrease upward from the dunites (42–45 wt.%) to the lherzolites (36–41 wt.%),
while Al2O3 and incompatible elements increase upward. In contrast, the Lower unit consists of coarse-grained dunites and lherzolites
containing 37–40 and 28–35 wt.% MgO, respectively. Sharp contacts between the Upper and Lower units and fine-grained dunite
xenoliths at the top of the Lower unit indicate that the Lower unit intruded along the base of the Upper unit. Disseminated
and net-textured sulfides primarily occur in the Lower unit and comprise the no. 24 ore body. Very low S contents (<100 ppm)
of the wall rocks at Jinchuan indicate that they were not the source of S causing sulfide immiscibility. Sulfide segregation
more likely occurred in deep-seated magma chambers, and sulfides were deposited in the Western intrusion when sulfide-bearing
magmas passed through the intrusion. In contrast, the Eastern intrusion was formed by injections of sulfide-free and sulfide-bearing
olivine-crystal mushes, respectively, from another deep-seated staging magma chamber. The Eastern and Western intrusions and
the deep-seated magma chambers comprise a complicated magma plumbing system at Jinchuan. Normal faults played a significant
role in the formation of the magma plumbing system and provided pathways for the magmas. 相似文献
54.
Trace and minor elements in sphalerite: A LA-ICPMS study 总被引:18,自引:0,他引:18
Nigel J. Cook Cristiana L. Ciobanu Allan Pring William Skinner Leonid Danyushevsky Frank Melcher 《Geochimica et cosmochimica acta》2009,73(16):4761-4791
Sphalerite is an important host mineral for a wide range of minor and trace elements. We have used laser-ablation inductively coupled mass spectroscopy (LA-ICPMS) techniques to investigate the distribution of Ag, As, Bi, Cd, Co, Cu, Fe, Ga, Ge, In, Mn, Mo, Ni, Pb, Sb, Se, Sn and Tl in samples from 26 ore deposits, including specimens with wt.% levels of Mn, Cd, In, Sn and Hg. This technique provides accurate trace element data, confirming that Cd, Co, Ga, Ge, In, Mn, Sn, As and Tl are present in solid solution. The concentrations of most elements vary over several orders of magnitude between deposits and in some cases between single samples from a given deposit. Sphalerite is characterized by a specific range of Cd (typically 0.2-1.0 wt.%) in each deposit. Higher Cd concentrations are rare; spot analyses on samples from skarn at Baisoara (Romania) show up to 13.2 wt.% (Cd2+ ↔ Zn2+ substitution). The LA-ICPMS technique also allows for identification of other elements, notably Pb, Sb and Bi, mostly as micro-inclusions of minerals carrying those elements, and not as solid solution. Silver may occur both as solid solution and as micro-inclusions. Sphalerite can also incorporate minor amounts of As and Se, and possibly Au (e.g., Magura epithermal Au, Romania). Manganese enrichment (up to ∼4 wt.%) does not appear to enhance incorporation of other elements. Sphalerite from Toyoha (Japan) features superimposed zoning. Indium-sphalerite (up to 6.7 wt.% In) coexists with Sn-sphalerite (up to 2.3 wt.%). Indium concentration correlates with Cu, corroborating coupled (Cu+In3+) ↔ 2Zn2+ substitution. Tin, however, correlates with Ag, suggesting (2Ag+Sn4+) ↔ 3Zn2+ coupled substitution. Germanium-bearing sphalerite from Tres Marias (Mexico) contains several hundred ppm Ge, correlating with Fe. We see no evidence of coupled substitution for incorporation of Ge. Accordingly, we postulate that Ge may be present as Ge2+ rather than Ge4+. Trace element concentrations in different deposit types vary because fractionation of a given element into sphalerite is influenced by crystallization temperature, metal source and the amount of sphalerite in the ore. Epithermal and some skarn deposits have higher concentrations of most elements in solid solution. The presence of discrete minerals containing In, Ga, Ge, etc. also contribute to the observed variance in measured concentrations within sphalerite. 相似文献
55.
Xiaozhi Yang Leonid Dubrovinsky M. A. G. M. Manthilake Qingguo Wei 《Physics and Chemistry of Minerals》2012,39(1):57-64
In situ Raman spectra of hydrous wadsleyite (β-Mg2SiO4) with ~1.5 wt% H2O, synthesized at 18 GPa and 1,400°C, have been measured in an externally heated diamond anvil cell up to 15.5 GPa and 673 K.
With increasing pressure (at room temperature), the three most intense bands at ~549, 720 and 917 cm−1 shift continuously to higher frequencies, while with increasing temperature at 14.5 GPa, these bands generally shift to lower
frequencies. The temperature-induced frequency shifts at 14.5 GPa are significantly different from those at ambient pressure.
Moreover, two new bands at ~714 and ~550 cm−1 become progressively significant above 333 and 553 K, respectively, and disappear upon cooling to room temperature. No corresponding
Raman modes of these two new bands were reported for wadsleyite at ambient conditions, and they are thus probably related
to thermally activated processes (vibration modes) at high-pressure and temperature conditions. 相似文献
56.
Past changes in the Arctic Ocean and its marginal seas have been profound, even during the last 10,000 years. Understanding these changes, such as those occurring during the transition from glacial to interglacial climates, are important for research on modern processes, because this knowledge provides a framework and unique perspective in which to view the modern physical and biological processes. This paper discusses our current understanding of past environmental change and processes relative to those currently in progress. Special emphasis is placed on the most recent transition from a glacial state to the modern interglacial conditions. 相似文献
57.
Vladimir V. Ivanov Igor V. Polyakov Igor A. Dmitrenko Edmond Hansen Irina A. Repina Sergey A. Kirillov Cecillie Mauritzen Harper Simmons Leonid A. Timokhov 《Deep Sea Research Part I: Oceanographic Research Papers》2009,56(1):1-14
A combination of 2-year-long mooring-based measurements and snapshot conductivity–temperature–depth (CTD) observations at the continental slope off Spitsbergen (81°30′N, 31°00′E) is used to demonstrate a significant hydrographic seasonal signal in Atlantic Water (AW) that propagates along the Eurasian continental slope in the Arctic Ocean. At the mooring position this seasonal signal dominates, contributing up to 50% of the total variance. Annual temperature maximum in the upper ocean (above 215 m) is reached in mid-November, when the ocean in the area is normally covered by ice. Distinct division into ‘summer’ (warmer and saltier) and ‘winter’ (colder and fresher) AW types is revealed there. Estimated temperature difference between the ‘summer’ and ‘winter’ waters is 1.2 °C, which implies that the range of seasonal heat content variations is of the same order of magnitude as the mean local AW heat content, suggesting an important role of seasonal changes in the intensity of the upward heat flux from AW. Although the current meter observations are only 1-year long, they hint at a persistent, highly barotropic current with little or no seasonal signal attached. 相似文献
58.
Anna Spivak Natalia Solopova Valerio Cerantola Elena Bykova Egor Zakharchenko Leonid Dubrovinsky Yuriy Litvin 《Physics and Chemistry of Minerals》2014,41(8):633-638
Magnesite, siderite and ferromagnesites Mg1?x Fe x CO3 (x = 0.05, 0.09, 0.2, 0.4) were characterized using in situ Raman spectroscopy at high pressures up to 55 GPa. For the Mg–Fe-carbonates, the Raman peak positions of six modes (T, L, ν4, ν1, ν3 and 2ν2) in the dependence of iron content in the carbonates at ambient conditions are presented. High-pressure Raman spectroscopy shows that siderite undergoes a spin transition at ~40 GPa. The examination of the solid solutions with compositions Mg0.6Fe0.4CO3, Mg0.8Fe0.2CO3, Mg0.91Fe0.09CO3 and Mg0.95Fe0.05CO3 indicates that with increase in the amount of the Fe spin transition pressure increases up to ~45 GPa. 相似文献
59.
We review petrologic observations of reaction textures from high-grade rocks that suggest the passage of fluids with variable alkali activities. Development of these reaction textures is accompanied by regular compositional variations in plagioclase, pyroxenes, biotite, amphibole and garnet. The textures are interpreted in terms of exchange and net-transfer reactions controlled by the K and Na activities in the fluids. On the regional scale, these reactions operate in granitized, charnockitized, syenitized etc. shear zones within high-grade complexes. Thermodynamic calculations in simple chemical systems show that changes in mineral assemblages, including the transition from the hydrous to the anhydrous ones, may occur at constant pressure and temperature due only to variations in the H2O and the alkali activities. A simple procedure for estimating the activity of the two major alkali oxides, K2O and Na2O, is imple- mented in the TWQ software. Examples of calculations are presented for well-documented dehydration zones from South Africa, southern India, and Sri Lanka. The calculations have revealed two end-member regimes of alkalis during specific metamorphic processes: rock buffered, which is characteristic for the precursor rocks containing two feldspars, and fluid-buffered for the precursor rocks without K-feldspar. The observed reaction textures and the results of thermodynamic modeling are compared with the results of available experimental studies on the interaction of the alkali chloride and carbonate-bearing fluids with metamorphic rocks at mid-crustal conditions. The experiments show the complex effect of alkali activities in the fluid phase on the mineral assemblages. Both thermodynamic calculations and experiments closely reproduce paragenetic relations theoretically predicted by D.S. Korzhinskii in the 1940s. 相似文献
60.
Jan Paav Ilja Knésl Anna Vymazalová Ivan Vavín Ludmila Ivanovna Gurskay Leonid Ruslanovich Kolbantsev 《地学前缘(英文版)》2011,2(1):81-85
The Polar Urals region of northern Russia is well known for large chromium (Cr)-bearing massifs with major chromite orebodies, including the Centralnoye I deposit in the Ray-Iz ultramafic massif of the Ural ophiolite belt. New data on platinum (Pt)-group elements (PGE), geochemistry and mineralogy of the host dunite shows that the deposit has anomalous iridium (Ir) values. These values indicate the predominance of ruthenium–osmium–iridium (Ru–Os–Ir)-bearing phases among the platinum-group mineral (PGM) assemblage that is typical of mantle-hosted chromite ores. Low Pt values in chromites and increased Pt values in host dunites might reflect the presence of cumulus PGM grains. The most abundant PGM found in the chromite is erlichmanite (up to 15 μm). Less common are cuproiridsite (up to 5 μm), irarsite (up to 4–5 μm), and laurite (up to 4 μm). The predominant sulfide is heazlewoodite, in intergrowth with Ni–Fe alloys, sporadically with pentlandite, and rarely with pure nickel. Based on the average PGE values and estimated Cr-ore resources, the Centralnoye I deposit can be considered as an important resource of PGE. 相似文献